Photoconductive composition

ABSTRACT

HIGH-SPEED HETEROGENEOUS PHOTOCONDUCTIVE COMPOSITIONS ARE PROVIDED WHICH CONTAIN TRITOLYLAMINE PHOTOCONDUCTOR N A POLYMERIC BINDER MATERAL WHICH CONTAINS A PARTICULATE DISCONTINUOUS PHASE CONTAINING A COMBINATION OF A PYRYLIUM DYE AND A POLYMERIC MATERIAL HAVING AN ALKYLIDENE DIARYLENE MOIETY IN A RECURRING UNIT. THESE COMPOSITIONS ARE SUITABLE FOR THE FORMATION OF ELECTROPHOTOGRAPHIC ELEMENTS WHICH CAN BE PREPARED BY FORMING SAID COMPOSITIONS ON A SUITABLE CONDUCTIVE SUPPORT.

United States Patent O 3,706,554 PHOTOCONDUCTIVE COMPOSITION Charles J. Fox and William A. Light, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y. No Drawing. Filed Mar. 24, 1971, Ser. No. 127,822 Int. Cl. G03g 5/06 US. Cl. 961.6 9 Claims ABSTRACT OF THE DISCLOSURE High-speed heterogeneous photoconductive compositions are provided which contain tritolylamine photoconductor in a polymeric binder material which contains a particulate discontinuous phase containing a combination of a pyrylium dye and a polymeric material having an alkylidene diarylene moiety in a recurring unit. These compositions are suitable for the formation of electrophotographic elements which can be prepared by forming said compositions on a suitable conductive support.

This invention relates to electrophotography, and in particular to photoconductive compositions and elements.

The process of xerography, as disclosed by Carlson in US. Pat. 2,297,691, issued Oct. 6, 1942, employs an electrophotographic element comprising a support material bearing a coating of a normally insulating material Whose electrical resistance varies with the amount of incident electromagnetic radiation it receives during an imagewise exposure. The element, commonly termed a photoconductive element, is first given a uniform surface charge, generally in the dark after a suitable period of dark adaptation. It is then exposed to a pattern of actinic radiation which has the effect of differentially reducing the potential of this surface charge in accordance with the relative energy contained in various parts of the radiation pattern. The differential surface charge or electrostatic latent image remaining on the electrophotographic element is then made visible by contacting the surface with a suitable electroscopic marking material. Such marking material or toner, whether contained in an insulating liquid or on a dry carrier, can be deposited on the exposed surface in accordance with either the charge pattern or discharge pattern as desired. Deposited marking material can then be either permanently fixed to the surface of the sensitive element by known means such as heat, pressure, solvent vapor, or the like, or transferred to a second element to which it can similarly be fixed. Likewise, the electrostatic charge pattern can be transferred to a second element and developed there.

Various photoconductive insulating materials have been employed in the manufacture of electrophotographic elements. For example, vapors of selenium and vapors of selenium alloys deposited on a suitable support and particles of photoconductive zinc oxide held in a resinous, film-forming binder have found wide application in the present-day document copying applications.

Since the introduction of electrophotography, a great many organic compounds have also been screened for their photoconductive properties. As a result, a very large number of organic compounds have been known to possess some degree of photoconductivity. Many organic compounds have revealed a useful level of photoconduction and have been incorporated into photoconductive compositions. Typical of these organic photoconductors are the triphenylamines and the triarylmethane leuco bases. Optically clear photoconductor-containing elements having desirable electrophotographic properties can be especially useful in electrophotography. Such electrophotographic elements can be exposed through a transparent Patented Dec. 19, 1972 base if desired, thereby providing unusual flexibility in equipment design. Such compositions, when coated as a film or layer on a suitable support, also yield an element which is reusable; that is, it can be used to form subsequent images after residual toner from prior images has been removed by transfer and/or cleaning.

A high speed heterogeneous or aggregate photoconductive system was developed by William A. Light which overcomes many of the problems of the prior art. This aggregate composition is the subject matter of copending application Ser. No. 804,266, filed Mar. 4, 1969, now US. Pat. 3,615,414, and entitled, Novel Photoc0n ductive Compositions and Elements. The addenda disclosed therein are responsible for the exhibition of desirable electrophotographic properties in photoconductive elements prepared therewith. In particular, they have been found to enhance the speed of many organic photoconductors when used therewith. The degree of such enhancement is, however, variable, depending on the particular organic photoconductor so used.

It is, therefore, an object of this invention to provide a novel photoconductive composition having unexpectedly high electrophotographic speeds.

It is another object of this invention to provide electrophotographic elements comprising the novel photoconductive composition of this invention.

These and other objects of the invention are accomplished through the use, in a heterogeneous composition of the type hereina-bove referred to, of photoconductors comprising tritolylamine having the methyl substituent para to the point of attachment of the phenyl ring to the nitrogen atom.

The heterogeneous multiphase compositions used in this invention comprise an organic sensitizing dye and an electrically insulating, film-forming polymeric material. They may be prepared by several techniques, such as, for example, the so-called dye first technique described in copending Gramza et al. application U.S. Ser. No. 816,- 831, filed Apr. 14, 1969, now US. Pat. No. 3,615,396, entitled, Method for the Preparation of Photoconductive Compositions. Alternatively, they may be prepared by the so-called shearing method described in copending Gramza application U.S. Ser. No. 821,513, filed May 2, 1969, now US. Pat. No. 3,615,415, entitled Method for the Preparation of Photoconductive Compositions. This latter method involves the high speed shearing of the photoconductive composition prior to coating and thus eliminates subsequent solvent treatment, as was disclosed in the Light application hereinabove referred to. By whatever method prepared, the heterogeneous composition is combined with the tritolylamine photoconductor in a suitable solvent to form a photoconductor-containing composition which is coated on a suitable support to form a separately identifiable multiphase composition, the heterogeneous nature of which is generally apparent when viewed under magnification, although such compositions may appear to be substantially optically clear to the naked eye in the absence of magnification. There can, of course, be a macroscopic heterogeneity. Suitably, the dye-contain ing aggregate in the discontinuous phase is predominantly in the size range of from about 0.01 to about 25 microns.

In general, the heterogeneous compositions formed as described herein are multiphase organic solids containing dye and polymer. The polymer forms an amorphous matrix or continuous phase which contains a discrete discontinuous phase as distinguished from a solution. The discontinuous phase is the aggregate species which is a cocrystalline complex comprised of dye and polymer.

The term co-crystalline complex as used herein has reference to a crystalline compound which contains dye and polymer molecules co-crystallized in a single crystalline structure to form a regular array of the molecules in a three-dimensional pattern.

Another feature characteristic of the heterogeneous compositions fomed as described herein is that the wavelength of the radiation absorption maximum characteristic of such compositions is substantially shifted from the wavelength of the radiation absorption maximum of a substantially homogeneous dye-polymer solid solution formed of similar constituents. The new absorption maximum characteristic of the aggregates formed by this method is not necessarily an overall maximum for this system as this will depend upon the relative amount of dye in the aggregate. Such an absorption maximum shift in the formation of multiphase heterogeneous systems for the present invention is generally of the magnitude of at least about nm. If mixtures of dyes are used, one dye may cause an absorption maximum shift to a long wavelength and another dye cause an absorption maximum shift to a shorter wavelength. In such cases, a formation of the heterogeneous compositions can more easily be identified by viewing under magnification.

It has been found according to this invention that the photoconductor-containing compositions described herein have unusual photographic properties and in particular have enhanced speed over closely related photoconductorcontaining compositions. These increases are observed when the coating accepts a suitable potential (e.g., 500- 600 volts) and the relative speed of the coating is determined on the basis of the reciprocal of the exposure required to reduce the potential of the surface charge by 100 volts (shoulder speed) or to 100 volts (toe speed). The terms shoulder speed and toe speed are terms known in the photographic art with reference to H and D curves. As used herein, such terms refer to corresponding curves resulting from exposure plotted against voltage. The reduction of the surface potential to 100 volts or below is significant in that it represents a requirement for suitable broad area development of an electrostatic image. The relative speed at 100 volts is a measure of the ability to produce and hence to develop or otherwise utilize the electrostatic image. When some conventional photoconductive elements are charged and exposed, the surface potential may not drop to or below 100 volts and therefore no speed can be assigned to such an element. Generally, photoconductors are used in photoconductive compositions which have the ability to exhibit a drop in surface potential to below 100 volts and thus a definite speed can be ascertained. The photoconductive compositions and elements of this invention measured accordingly have unexpectedly enhanced electrophotographic speeds.

The high speeds associated with the compositions, elements and methods of the invention are maintained even at relatively high concentrations of photoconductor in the composition. When triarylamines having fewer substituents are used, in general, the speed increases to a maximum at a certain relatively low concentration of photoconductor, and thereafter, typically decreases. The use of tri-p-tolylamine, unexpectedly, permits the use of considerably higher concentrations of photoconductor in the coating composition than does the use of triarylamines having methyl substituents on less than all of the phenyl nuclei. The use of alkyl groups larger than methyl as substituents does not produce the high speeds associated with the elements and compositions of this invention. Illustrative of such larger groups are ethyl groups and n-butyl groups. The large increase in speed obtained with the specific combination of materials described herein is unique in that related combinations not including those of the invention do not show corresponding large speed increases.

Sensitizing dyes and electrically insulating polymeric materials are used in forming these heterogeneous compositions. Typically, pyrylium dyes, including pyrylium, bispyrylium, thiapyrylium and selenapyrylium dye salts and also salts of pyrylium compounds containing condensed ring systems such as salts of benzopyrylium and naphthopyrylium dyes are useful in forming such compositions. Dyes from these classes which may be useful are disclosed in copending application of Light, U.S. Ser. No. 804,266, filed Mar. 4, 1969, and corresponding Belgian Pat. 746,328, dated Apr. 30, 1970.

Particularly useful dyes in forming the feature aggregate are pyrylium dye salts having the formula:

wherein:

R and R can each be phenyl radicals, including substituted phenyl radicals having at least one substituent chosen from alkyl radicals of from 1 to about 6 carbon atoms and alkoxy radicals having from 1 to about 6 carbon atoms;

R can be an alkylamino-substituted phenyl radical having from 1 to 6 carbon atoms in the alkyl moiety, and including dialkylamino-substituted and haloalkylaminosubstituted phenyl radicals;

X can be an oxygen or a sulfur atom; and

Z- is the same as above.

The polymers useful in forming the aggregate compositions include a variety of materials. Particularly useful are electrically insulating, film-forming polymers having an alkylidene diarylene moiety in a recurring unit such as those linear polymers, including copolymers, containing the following moiety in a recurring unit:

wherein:

R and R when taken separately, can each be a hydrogen atom, an alkyl radical having from one to about 10 carbon atoms such as methyl, ethyl, isobutyl, hexyl, heptyl, octyl, nonyl, decyl, and the like including substituted alkyl radicals such as trifluoromethyl, etc., and an aryl radical such as phenyl and naphthyl, including substituted aryl radicals having such substituents as a halogen atom, an alkyl radical of from 1 to about 5 carbon atoms, etc.; and R and R when taken together, can represent the carbon atoms necessary to complete a saturated cyclic hydrocarbon radical including cycloalkanes such as cyclohexyl and polycycloalkanes such as norbornyl, the total number of carbon atoms in R and R being up to about 19;

R and R; can each be hydrogen, an alkyl radical of from 1 to about 5 carbon atoms, e.g., or a halogen such as chloro, bromo, iodo, etc. and

R is a divalent radical selected from the following:

Preferred polymers useful in the present method of forming aggregate crystals are hydrophobic carbonate polymers containing the following moiety in a recurring unit:

wherein:

Each R is a phenylene radical including halo substituted phenylene radicals and alkyl substituted phenylene radicals; and R and R are as described above. Such compositions are disclosed, for example in US. Pat. Nos. 3,028,365 and 3,317,466. Preferably polycarbonates containing an alkylidene diarylene moiety in the recurring unit such as those prepared with Bisphenol A and including polymeric products of ester exchange between diphenylcarbonate and 2,2-bis-(4-hydroxyphenyl)propane are useful in the practice of this invention. Such compositions are disclosed in the following US. Pats.: US. 2,999,750 by Miller et al., issued Sept. 12, 1961; 3,038,874 by Laakso et al., issued June 12, 1962; 3,038,879 by Laakso et al., issued June 12, 1962; 3,038,880 by Laakso et al., issued June 12, 1962; 3,106,544 by Laakso et al., issued Oct. 8, 1963; 3,106,545 by Laakso et al., issued Oct. 8, 1963, and 3,106,546 by Laakso et al., issued Oct. 8, 1963. A wide range of film forming polycarbonate resins are useful, with completely satisfactory results being obtained when using commercial polymeric materials which are characterized by an inherent viscosity of about 0.5 to about 1.8.

The following polymers are included among the ma- 9 Poly[4,4"isopropylidenebis(2-methylphenylene)carbonate]. 10 Poly(4,4-isopropylidenediphenylene-co-1,4-phenylene carbonate).

11 Poly(4,4-isopropylidencdiphenylenecod,B-phenylene carbonate).

12. Poly(4,4-isopropylidenediphenylene-co-4,4-diphenylene carbonat 13 Poly(4,4-isopropylidenediphenylene-co4,4-oxydiphenylene carbonate) 14 Poly(4,4-is0propylidenediphenylene-co-4,4'-carbonyldiphenylene carbonate 15 Poly(4,4-isopropylidenediphenylene-c0-4,4-ethy1enediphenylene carbonate 16. Poly[4,4-methylenebis(2-methylphenylene)carbonate].

17... Po1y[1,1-(p-bromophenylethylidene)bis(1,4-phenylene) carbonate].

18..." Poly[4,4-isopropylidenediphenylene-co-4,4-sultonyldiphenylene) carbonate].

19 Poly[4,4'-cyclohexanylidene(4-diphenylene) carbonate].

Poly[4,4-isopropylidcnebis(2-chlorophenylene) carbonate].

P0ly(4,4-hexafluoroisopropylidenediphenylene carbonate).

Poly(4,4-isopropylidenediphenylene 4,4-isopropylidenedibenzoate).

23 Poly(4,4-isopropylidenedibenzyl 4,4-isopropylidenedibenzoate).

24 Poly[4,4-(1,2-dimethylpropylidene)diphenylene carbonate].

25.--" Poly[4,4-(1,2,2-trimethy1pr0pylidene) diphenylene carbonate].

26 Polyl4,4-[1-(a-naphthyl)ethylidene1d1phenylene carbonate Poly[4,4-(1,3-dimethylbutylidene)diphenylene carbonate]. 28.- Po1y[4,4-(2-norbornylidene)diphenylene carbonate]. 29 Poly[4,4-(hexahydro-4,7-methanoindan-5-ylidene) diphenylene carbonate].

Electrophotographic elements of the invention can be prepared in the conventional manner, i.e., by blending a dispersion or solution of the photoconductive composition together with a binder, when necesary or desirable, and coating or forming a self-supporting layer with the materials. Supplemental materials useful for changing the spectral sensitivity or electrophotosensitivity of the element can be added to the composition of the element when it is desirable to produce the characteristic effect of such materials. If desired, other polymers can be incorporated in the vehicle, for example, to alter physical properties such as adhesion of the photoconductive layer to the support and the like. Techniques for the preparation of heterogeneous photoconductive layers containing such additional vehicles are described in copending application of C. L. Stephens Ser. No. 89,447 filed Nov. 13, 1970, and entitled, Method of Forming Heterogeneous Photoconductive Compositions and Elements. The photoconductive layers of the invention can also be sensitized by the 75 addition of effective amounts of sensitizing compounds to exhibit improved electrophotosensitivity.

The amount of tritolylamine photoconductor incorporated into the photoconductive compositions and elements of the invention can be varied over a relatively wide range. Thus, for example, the lower limit is determined by the amount required to give a desired photoconductive response, while the upper limit is determined by the solubility limit or by the concentration beyond which no further enhancement of electrophotographic response is obtained. The useful range of concentration may thus extend from appreciably less than one mole of photoconductor per 1000 grams of polymer to in excess of six moles per 1000 grams of polymer. A preferred range is from about three moles to about six moles of photoconductor per 1000 grams of polymer.

Solvents useful for preparing coating compositions with the photoconductors of the present invention can include a Wide variety of organic solvents for the components of the coating composition.

Typical solvents include:

(1) Aromatic hydrocarbons such as benzene, naphthalene, etc., including substituted aromatic hydrocarbons such as toluene, xylene, methylene, etc.;

(2) Ketones such as acetone, Z-butanone, etc.;

(3) Halogenated aliphatic hydrocarbons such as methylene chloride, chloroform, ethylene chloride, etc.;

(4) Ethers including cyclic ethers such as tetrahydrofuran, ethylether;

(5) Mixtures of the above.

In preparing the photoconductive coating compositions of the present invention useful results are obtained where the photoconductor is present in an amount equal to at least about 0.1 weight percent of the coating composition. The upper limit in the amount of photoconductive material present can be widely varied to at least by weight in accordance with usual practice.

Suitable supporting materials for coating sensitizercontaining photoconductive layers in accordance with the method of this invention can include any of a wide variety of electrically conducting supports, for example, paper (at a relative humidity above 20 percent); aluminumpaper laminates; metal foils such as aluminum foil, zinc foil, etc.; metal plates, such as aluminum, copper, zinc, brass and galvanized plates; vapor deposited metal layers such as silver, nickel, aluminum and the like coated on paper or conventional photographic film bases such as cellulose acetate, polystyrene, etc. Such conducting materials as nickel can be vacuum deposited on transparent film supports in sufiiciently thin layers to allow electrophotographic elements prepared therewith to be exposed from either side of such elements. An especially useful conducting support can be prepared by coating a support material such as poly(ethylene terephthalate) with a conducting layer containing a semiconductor dispersed in a resin or vacuum deposited on the support. Such conducting layers both with and without insulating barrier layers are described in US. Pat. 3,245,833 by Trevoy, issued Apr. 12, 1966. Likewise, a suitable conducting coating can be prepared from the sodium salt of a carboxyester lactone of maleic anhydride and a vinyl acetate polymer. Such kinds of conducting layers and methods for their optimum preparation and use are disclosed in US. 3,007,- 901 by Minsk, issued Nov. 7, 1961 and 3,262,807 by Sterman et al., issued July 26, 966.

Coating thicknesses of the photoconductive composition of the support can vary widely. Normally, a coating in the range of about 10 microns to about 300 microns before drying is useful for the practice of this invention. The preferred range of coating thickness is found to be in the range from about 50 microns to about microns before drying, although useful results can be obtained outside of this range. The resultant dry thickness of the coating is preferably between about 2 microns and about 50 microns, although useful results can be obtained with a dry coating thickness between about 1 and about 200 microns.

After the photoconductive elements prepared according to the method of this invention have been dried, they can be employed in any of the well-known electrophotographic processes which require photoconductive layers. One such process is the xerographic process. In a process of this type, an electrophotographic element is held in the dark and given a blanket electrostatic charge by placing it under a corona discharge. This uniform charge is retained by the layer because of the substantial dark insulating property of the layer, i.e., the low conductivity of the layer in the dark. The electrostatic charge formed on the surface of the photoconductive layer is then selectively dissipated from the surface of the layer by imagewise exposure to light by means of a conventional exposure operation such as, for example, by a contact printing technique, or by lens projection of an image, and the like, to thereby form a latent electrostatic image in the photoconductive layer. Exposing the surface in this manner forms a pattern of electrostatic charge by virtue of the fact that light energy striking the photoconductor causes the electrostatic charge in the light struck areas to be conducted away from the surface in proportion to the intensity of the illumination in a particular area.

The charge pattern produced by exposure is then developed or transferred to another surface and developed there, i.e., either the charged or uncharged areas rendered visible, by treatment with a medium comprising electrostatically responsive particles having optical density. The developing electrostatically responsive particles can be in the form of a dust, i.e., powder, or a pigment in a resinous carrier, i.e., toner. A preferred method of applying such toner to a latent electrostatic image for solid area development is by the use of a magnetic brush. Methods of forming and using a magnetic brush toner applicator are described in the following U.S. Pats. 2,786,439 by Young, issued Mar. 26, 1957; 2,786,440 by Giaimo, issued Mar. 26, 1957; 2,786,441 by Young, issued Mar. 26, 1957; 2,874,063 by Greig, issued Feb. 17, 1959. Liquid develop ment of the latent electrostatic image may also be used. In liquid development, the developing particles are carried to the image-bearing surface in an electrically insulating liquid carrier. Methods of development of this type are widely known and have been described in the patent literature, for example, U.S. Pat. 2,907,674 by Metcalfe et al., issued Oct. 6, 1959. In dry developing processes, the mose widely used method of obtaining a permanent record is achieved by selecting a developing particle which has as one of its components a low-melting resin. Heating the powder image then causes the resin to melt or fuse into or on the element. The powder is, therefore, caused to adhere permanently to the surface of the photoconductive layer. In other cases, a transfer of the electrostatic charge image formed on the photoconductive layer can be made to a second support such as paper which would then become the final print after development and fusing. Techniques of the type indicated are well known in the art and have been described in the literature such as in RCA Review, vol. (1954), pages 469-484.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 A series of coating dopes having the following composition is prepared:

Dye-2,6-diphenyl 4 (4-dimethylaminophenyl)- Photoconductor--see below.

The sensitizing dye is added to the solvent and stirred for about two hours. The polymer is then added to the dye Cit solution with stirring for an additional two hours. The photoconductor is next added and the completed solution stirred rapidly for about one-half hour. Twelve dopes are prepared in all, each of four series of three containing one of the four photoconductors listed below in amounts of 2.25, 6.75 and 13.50 grams.

A-Triphenylamine B--Diphenyl-ptolylamine C'Phenyl-di-p-tolylamine D-Tri-p-tolylamine Each of the dopes is filtered through a 2- to S-micron rated fiber filter cartridge (Fulfio cartridge, Commercial Filter Corp). The filtered solutions are then each coated on a separate piece of poly(ethylene terephthalate) film support bearing a vapor deposited thin conducting layer of nickel. The thickness of the coating is from about 10 to about 12 microns. After drying each of the resultant elements is electrostatically charged under a corona source until the surface potential, as measured by an electrometer probe, reaches about 600 volts. The charged element is then exposed to a 3000 K. tungsten light source through a stepped density gray scale and also through a short wavelength pass interference filter having 30% transmittance at 600 m The exposure causes reduction of the surface potential of the element under each step of the gray scale from its initial potential, V to some lower potential, V, whose exact value depends upon the actual amount of exposure in meter-candle-seconds received by the area. The results of these measurements are then plotted on a graph of surface potential V vs. log exposure for each step. The actual speed of the photoconductive composition can then be expressed in terms of the reciprocal of the exposure required to reduce the surface potential to any fixed, selected value. Herein, unless otherwise stated, the actual negative speed is the numerical expression of 10 divided by the exposure in meter-candleseconds required to reduce the 600 v. charged surface potential to a value of v. Speeds thus determined are referred to as negative 100 v. toe speeds. The toe speeds are plotted on a graph of speed vs. concentration of photoconductor per 1000 moles of polymeric binder, and curves representing the best fit are drawn through the plotted points. The speeds shown in Table 2 below are read from these curves.

TABLE 2 Negative 100 volt toe speed Organic photoconductor 1 l 1 2 1 3 1 4 1 5 1 6 Compound A (outside this inventio 290 330 330 290 Compound B (outside this inventlOn 140 220 330 430 510 600 Compound 0 (outside this inventlon 370 670 900 1,030 1,050 950 CompoundD (of th1s1nvent1on) 350 .630 940 1, 240 1,530 1,850

L Concentration is expressed in moles of photoconductor/1,000 grams exan.

It is thus seen that Compound D (tri-p-tolylamine), when used in the dye polymer aggregate system described, uniquely gives an unexpected increase in speed which is maintained as concentration is increased; whereas the other compounds in general give either decreases in speed when the concentration is increased above certain low levels or an increase of a much lower order.

EXAMPLE 2 magnetic stirrer for about two hours. Three ml. of the first solution and all of the second solution are added to a combination of 0.92 g. of binder and 0.8 g. of photoconductor, and stirred until all of the solids are dissolved, to form a coating composition. The binder is Vitel PE-lOl polyester, a trademark of Goodyear Tire and Rubber, believed to be poly(4,4' isopropylidenebisphenyleneoxyethylene-co-ethylene terephthalate), 50:50 mole percent. The procedure is followed for each of the photoconductors listed in Table 3 below. Each of the coating compositions is then coated at a wet thickness of 100 microns on a nickel-bearing film support of the type described in Example 1 to form an electrophotographic element. The resulting elements are each, in turn, charged positively and exposed as in Example 1 except that no interference filter is used. The speed obtained as shoulder speed is read at a potential of 100 v. below the initial potential, and is given in Table 3 below.

The photoconductors are identified in Example 1. It is seen that the speed of Compound D in the composition of this invention is appreciably greater than that of analogous compounds which are substituted with a methyl group on less than all of the phenyl nuclei of triphenylamine.

EXAMPLE 3 A first solution is prepared by adding 0.08 g. of Dye 1 of Example 2 to 28.6 ml. of dichloromethane and stirring for about two hours, and thereafter adding 3.96 g. of Lexan 145 (see Example 2) and continuing stirring for an additional hour. The resulting solution is sheared in a high-speed blender for 30 minutes at a temperature of 20 C. A second solution is prepared by dissolving 0.3 g. of Dye 1 in 102 ml. of dichloromethane and stirring with a magnetic stirrer for about two hours. A coating formulation is prepared by mixing 7.7 g. of the first solution, 4.5 g. of the second solution, 0.25 g. of Lexan 145 and 0.25 g. of photoconductor as indicated in Table 4 below until all of the solids are dissolved. Each of the coating formulations is coated on a nickel-bearing film support as in Example 1 to form an electrophotographic element. The resulting elements are each charged positively and exposed as in Example 1 except that no interference filter is used. The speeds obtained as shoulder speeds and toe speeds are read at potentials of 100 v. below the initial potential V and at 100 v. above zero volts, respectively, The speeds are given in Table 4 below.

TABLE 4 Speed Photoconductor Shoulder Toe Tri-p-tolylamine 9, 500 1, 100 Tri-4-othylphenylamine 1 3, 200 1 310 Tri (4-n-butylphenyl) amine 3, 200 360 X This element would only charge to 270 volts. (V o) Clearly, the triphenylamine bearing methyl substituents on the three phenyl nuclei gives substantially higher speed to an element containing it in association with the aggregate material of Light than do other analogous photoconductors bearing higher alkyl substituents.

EXAMPLE 4 10 1965, entitled, Material for Electrophotographic Purposes. Electrophotographic elements and then prepared according to Example 1. When tested according to the procedure of Example 3, speeds are obtained as shown in Table 5 below.

TABLE 5 Speed Photoeonductor Shoulder Toe Tri-p-tolylamine 9, 500 1,100 Tri-p-bromophenylamine 2, 800

Two coating formulations are then made, each containing 0.25 g. of photoconductor, 1.00 g. of poly(4,4-isopropylidenebisphenyleneoxyethylene-co-ethylene terephthalate) and 0.002 gram of the dye 2,6-bis(4-ethylphenyl)- 1 TABLE 6 Speed Photoconductor Shoulder Toe Tri-p-tolylamine It is thus seen that elements containing tri-p-tolylamine uniquely have greatly enhanced speed when used in conjunction with the aggregate material over similar ele ments containing tri-p-bromophenylamine, and that the unexpectedly high speed difference is not produced in the absence of the aggregate material.

The invention has been described in detail with particular reference to preferred embodiments thereof, but, it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. A heterogeneous photoconductive composition comprising an electrically insulating polymeric material having an alkylidine diarylene moiety in a recurring unit, a pyrylium dye which has been solubilized with said polymeric material and at least 0.1% by weight of tri-p-tolylamine photoconductor, said composition being in the form of a multiphase organic solid having therein a particulate discontinuous phase containing a combination of said dye and polymeric material, the individual portions of said discontinuous phase having a size of about 0.01 to 25 microns, and said composition having a maximum radiation absorption at a wavelength at least about 10 my. different from the wavelength of maximum absorption of said dye solubilized with said polymeric material in a homogeneous composition.

2. A heterogeneous photoconductive composition comprising tri-p-tolylamine photoconductor, an electrically insulating carbonate resin having an alkylidene diarylene moiety in a recurring unit and an organic dye selected from the group consisting of a thiapyrylium, a pyrylium and a selenapyrylium dye salt which has been solubilized with said carbonate resin, a discontinuous phase of said composition comprising a combination of said dye and carbonate resin, the individual portions of said discontinuous phase having a size of about 0.01 to about 25 microns, said composition having a radiation wavelength range of absorption different than the wavelength range of absorption of a homogeneous composition comprised of a substantially homogeneous combination of said dye solubilized in said carbonate resin.

wherein:

R and R are aryl radicals selected from the group consisting of phenyl and substituted phenyl having at least one substituent selected from the group consisting of an alkyl radical of from 1 to about 6 carbon atoms and an alkoxy radical of from 1 to about 6 carbon atoms;

R is an alkylamino-substituted phenyl radical having from 1 to about 6 carbon atoms in the alkyl moiety;

X is selected from the group consisting of sulfur and oxygen; and

Z- is an anion.

4. The composition as described in claim 2 wherein said carbonate resin contains the following moiety in a recurring unit:

wherein:

each of R and R when taken separately, is selected from the group consisting of a hydrogen atom, an alkyl radical of from 1 to about carbon atoms and a phenyl radical, and R and R when taken together, are the carbon atoms necessary to form a cyclic hydrocarbon radical, the total number of carbon atoms in R and R being up to 19; and

R, and R are each selected from the group consisting of hydrogen, alkyl radicals of from 1 to about 5 carbon atoms, alkoxy radicals of from 1 to about 5 carbon atoms and a halogen atom.

5. A heterogeneous photoconductive composition comprising a continuous binder phase containing at least 0.1% by weight tri-p-tolylamine photoconductor, said continuous phase having dispersed therein a sensitizing amount of a co-crystalilne complex of (a) a dye selected from the group consisting of a 2,4,6-substituted pyrylium dye salt and a 2,4,6-substituted thiapyrylium dye salt and (b) a carbonate polymer having an alkylidene diarylene moiety in a recurring unit, said complex having a particle size of about .01 to about 25 microns and a radiation absorption maximum different from a solid solution of said dye and polymer.

6. An electrophotographic element comprising a conductive support having coated thereon the photoconductive composition as described in claim 1.

7. An electrophotographic element comprising a conductive support having coated thereon the photoconductive composition as described in claim 2.

8. In an electrophotographic process wherein an electrostatic charge pattern is formed on a photoconductive element, the improvement wherein said element is comprised of an electrically conducting support having coated thereon a photoconductive layer as described in claim 6.

9. An electrophotographic element comprising a conductive support having thereon a layer of a photoconductive composition comprising a continuous binder phase containing at least 0.1% by weight of tri-p-tolylamine photoconductor, said continuous phase having dispersed therein a sensitizing amount of a co-crystalline complex a of a 2,4,6-substituted thiapyrylium dye salt and po1y(4,4'-

References Cited UNITED STATES PATENTS 3,180,730 4/1965 Kliipsel et a1 96] 3,387,973 6/1968 Fox et a1. 961.5 3,591,374 7/1971 Seus 96l.6 3,615,396 10/1971 Gramza 96-1.6 3,615,414 10/1971 Light 961.6 3,615,415 l0/1971 Gramza 96-1.6

CHARLES E. VAN 'HORN, Primary Examiner M. B. WITTENBERG, Assistant Examiner US. Cl. X.R.

961.5; 252-501; 260-37 PC, 327 TH, 345.1 

